c# - Autofac and Keyed registrations - the proper behavior? -

the question rather basic, started use autofac , encountered issue autofac not work expected work. given "that's way works" understand logic behind such behavior. here basic code:

public interface x { }  internal class : x { }  class program {     static void main(string[] args)     {         var builder = new containerbuilder();         builder.registertype<a>().keyed<x>("a");         ilifetimescope scope = builder.build();          try         {             var instance = scope.resolve<x>();         }         catch (exception e)         {             console.writeline(e);             throw;         }     } } 

the attempt resolve result in error (exception). why ? indeed did not asked resolve specific keyed , calling

var instance = scope.resolvekeyed<x>("a"); 

would work , resolve expected, if register

builder.registertype<a>().keyed<x>("a").as<x>(); 

but why not resolve if did not asked specific keyed ? mean logic expected - ask specific - resolve specific, if did not ask specific - resolve any/last registered .

so why behavior selected default.

services registered keyed service resolvable using key. if want resolve service without using key, has registered without 1 using .as<...>(). register components both if wish them resolve using key or default.

to use analogy, can have door 2 kinds of handles: 1 lock, or 1 without. if want open keyed door, need supply key. door without lock doesn't require key.